Sheldon: Can I invite you in for tea?
Professor Proton: No, I really have to run .
*Penny walks in the room*
Penny: Hey Arthur, how are you?
Professor Proton: Well I guess one cup wouldn't hurt.

Professor Proton: (To Penny) So, you have any single grandmothers?
Penny: Sorry, they're both married.
Professor Proton: Good. .... Happily?

Penny: What are you working on?
Sheldon: Can't talk. In the zone.
Penny: (To Amy) Do you know what he's doing?
Amy: Could be anything. Last time he was like this he figured out electron transport in graphene. The time before that he was making a list of who's allowed in his tree fort if he ever gets one. Still can't believe I didn't make the cut.

Penny: Sheldon, you wanna take a break? Your food's ready.
Leonard: What are you doing? He's both happy and quiet. It's like seeing a unicorn and big foot at the same time.

Bernadette: Great news. A raccoon virus just crossed the species barrier and can now infect humans.
Raj: Why is that great news?
Bernadette: In the pharmaceutical business we have a saying: mo' infections, mo' money.

Penny: Aww, what horrible thing are you trying to make up for?
Howard: Just putting something in the bank for what horrible thing I do next.

Penny: How come you've never done anything romantic to celebrate our first date?
Leonard: For starters, you've broken up with me so many times, which first date are we talking about?
Sheldon: Oh, somebody call the burn ward. ... And back to the zone.

Leonard: Besides, can you even name one romantic thing you've done for me?
Penny: I can name tons.
Leonard: And sex doesn't count.
Penny: Oh.

Penny: Just you wait and see. I'm gonna romance your freakin' ass off.
Leonard: That's beautiful. Is that Shakespeare?

Howard: So I'm almost done writing the song for Bernadette. Are you cool playing the cello?
Leonard: If by cool you mean willing to, yes. If by cool you mean cool, clearly you've never seen me play the cello.

Howard: (To Raj) Will you play the ukelele?
Raj: Sure, I'd be happy to shred it on my axe.
Howard: Or you could just play your tiny, ridiculous guitar.

Sheldon: They called it the greatest thing since the Communist party. Although I'm pretty sure the Communist party made them say that. I like China. See, they know how to keep people in line.

Sheldon: Don't worry. I will remain the same down to earth, humble Joe I've always been.
Leonard: Good to know.
Sheldon: Now give me that cookie, I discovered an element.

Raj: As I'm sure you're aware the quickest way to a man's heart is through his -
Penny: Pants. But Leonard said sex doesn't count.
Raj: You poor thing. You have one arrow in your quiver and you just can't use it.

Penny: I don't know if I wanna cook for him. He's kind of a picky eater. "It's too salty. It's too dry. It's too burnt and frozen at the same time."